1. Field of the Invention
The present invention relates to a resin composition for purging contaminants in a plastic processing machine.
2. Description of the Related Art
Plastics have excellent properties such as easy processability, high productivity, light weight and relative low procuring costs, so they are used for the parts and structural materials for automobiles, autobicycles, scooters, televisions, radios, audio equipment, washing machines, rice cookers, personal computers, portable telephones, game machinery, building materials, office supplies, stationery, toys, sports goods, sports equipment, agricultural tools and marine tools.
These products are usually prepared by plastic processing methods such as injection molding, blow molding, compression molding, transfer molding, rotating molding, slush molding, inflation tubular film process, and extrusion molding.
As plastics processing are conducted at high temperatures above 200° C., additives, monomers, decomposed materials in the plastics are changed to carbonized materials such as tar, pitch and other colored sticky substances, which are apt to adhere to the surface of the screw, barrel and die of the plastic processing machine to cause transfer of the carbonized materials to the molded product.
The above mentioned transfer makes the surfaces of molded products dirty and makes the dimensions of the molded products inaccurate, resulting in failure to perform expected moving or structual functions, therefore cleaning the screw, barrel and die of the plastic processing machine has been required.
In case of production changes from specific colored molded articles to non-colored or other colored molded articles, cleaning the screw, barrel and die has been also required to avoid crosscontamination caused by specifically colored resin compound residue.
However, there are some problems with the conventional method of cleaning the screw, barrel and die.
One conventional cleaning method involves dismantling the plastic processing machine, resulting in exposing the screw, barrel and die the outside. Then the carbonized material or colored materials adhered to the surface of the screw, barrel and die is removed using a separating tool such as knife.
However, this method has a defect of exposing operators to high temperatures for long times, which often causes some operators to suffer skin burns or electric shock.
In the case of large sized plastic processing machines, dismantling is impossible.
There are known other conventional cleaning methods in which uncolored thermoplastic resin such as low density polyethylene is passed through the inside of plastic processing machines.
However such methods cannot remove contaminants entirely even if used over extended times. Moreover, such methods generate a large amount of mixed product consisting of contaminants and resin, which scarcely find use as a recycled resin compound.
Another cleaning method involves using a resin composition containing an inorganic powder such as calcium carbonate which exerts improved effects on the removal of colored contaminants.
However, this method causes new problems of the inorganic power remaining in the plastic processing machine.
Another cleaning method also has attempted to use a resin composition consisting of a thermoplastic resin such as low density polyethylene and a surface active agent such as sodium stearate or polyoxyethylene nonylphenyl ether having the effect of lowering interface tension. However, the colored contaminants were scarcely removed.
Based on the above mentioned knowledge, new cleaning methods have been disclosed in Japanese Kokai Patents (H2180941 and H753774), in which a resin composition consisting of uncolored thermoplastic resin and a calcium salt of an organic boron compound having SP3 hybridization orbitals. This resin composition maintains a certain amount of abrasive properties.
However, the method does not exert a sufficient effect of removing colored contaminants.